Correction table creation method for head position control, head position control method and disk device

ABSTRACT

A head position control system control the position of the head by correcting the components synchronizing rotation of the disk from the head control amount, in which an adjusted gain to minimize the components synchronizing rotation after correction is theoretically acquired. An adjusted gain based on the ratio of the magnitude between the components synchronizing rotation of a disk and the components not synchronizing rotation of the disk in the position signals is used. And a gain to minimize RRO after correction can be theoretically determined using an expression to determine RRO after correction. The gain can be determined without depending on experiment, and the value of RRO after correction can be guaranteed, therefore the manufacturing time and the device specifications can be determined.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2004-263631, filed on Sep. 10,2004, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a correction table creation method forhead position control for a disk device which controls the position of ahead to a rotating disk for one or both of reading and writinginformation from/to the disk, and head position control method and thedisk device thereof, and more particularly to a correction tablecreation method for head position control for correcting the rotationsynchronization component of the position signals, and the head positioncontrol method and disk device thereof.

2. Description of the Related Art

Disk storage devices for recording to and regenerating from a rotatingdisk medium are widely used as the storages of data and otherinformation. A disk device is comprised of a disk for storing data, aspindle motor for rotating the disk, a head for recording/regeneratinginformation to/from the disk, and an actuator for moving the head to atarget position. Typical examples are magnetic disk devices (HDD: harddisk drive) and magneto-optical disk devices (DVD-ROM, MO).

In a magnetic disk device, a plurality of position signals for detectingthe position of the head are recorded in an arc with respect to therotation center and form a track. A position signal is comprised of aservo mark, track number (gray code) and offset information. The currentposition of the head can be known by the track number and offsetinformation.

The difference between this position information and target position isdetermined, calculation is performed according to the displacementamount, and drive signals for driving the actuator, such as current fora VCM (Voice Coil Motor) and voltage for a piezo actuator, are supplied.

The position signal (servo signal) on the disk is either recorded by thedisk device itself with use of the STW (Servo Track Writing) method, orrecorded by an external STW device. The STW method for recording theposition signals by the disk device itself includes pushpin STW,self-servo writing and rewrite STW. The method for recording by anexternal STW device includes a method for recording on a single disk,magnetic transfer and discrete medium.

In order to accurately record and regenerate data, it is necessary toaccurately position the head to the position demodulated from theposition signals. But the position signals include noise, whichdeteriorates the positioning accuracy. This noise has a componentsynchronizing with the rotation of the spindle motor, and a componentnot synchronizing with the rotation. The component synchronizing withthe rotation can be measured and corrected, and can be suppressed tozero if the measurement is allowed. For the component not synchronizingwith rotation, on the other hand, measurement and correction aredifficult. Various methods have been proposed to measure and correct thecomponent synchronizing the rotation.

There are two causes that generate the component synchronizing with therotation of the spindle motor in the position signals in a status wherevibration is not received from the outside. The first cause is that theservo signals are not accurately recorded concentrically during STW. Aslong as the servo signals are mechanically recorded, mechanical,electrical and magnetic noises during recording are unavoidable.Therefore accurately recording the servo signals concentrically duringSTW is extremely difficult.

The second cause is that distortion occurs to the disk and spindle motorafter STW. Microscopically, the position signals are not alignedconcentrically with respect to the center of rotation of the spindlemotor. The track width of current disk devices is around 200 nano meter,so the influence even of a slight distortion on positioning accuracy isextremely large.

The component of fluctuation of the position signals that synchronizethe rotation is called “eccentricity” or “RRO (Repeatable Run Out)”, andthe component of a one time rotation frequency is called “primary”, andtwo times thereof is called “secondary”. If RRO occurs, the positioningaccuracy of the head deteriorates, which causes problems in recordingand regenerating data. For example, if the positioning accuracy is poor,when data is recorded on a track, a part of previously recorded data onthe adjacent tracks is overwritten. To prevent such a status, RRO mustbe controlled in positioning control.

Conventionally available methods of controlling RRO are a method ofcontrolling the actuator not to follow-up RRO but to ignore it, as shownin FIG. 42, and a control method of controlling the actuator tofollow-up RRO, as shown in FIG. 43.

FIG. 42 and FIG. 43 show block diagrams of the head position controlsystem, where as a disturbance is applied to the control system, thecomponents synchronizing the rotation of the spindle motor and thecomponents not synchronizing the rotation thereof are indicated as RRO,NRRO, RPE and NRPE. RRO (Repeatable Run Out) is a component ofpositional disturbance synchronizing rotation. NRRO (Non-Repeatable RunOut) is a component of positional disturbance not synchronizingrotation. RPE (Repeatable Position Error) is a component synchronizingrotation included in the position error ‘e’ when the positioning controlis performed. And NRPE (Non-Repeatable Position Error) is a componentnot synchronizing rotation included in the position error ‘e’ when thepositioning control is performed. The RRO and RPE, which are componentssynchronizing rotation, indicate different values depending on thesample of the servo.

To perform positioning control, it is necessary to know RRO, RPE andRPE+RRO, and to minimize all these three values. RRO indicates thedistortion of the track on the disk. Here the difference from RRO of theadjacent track is critical. This difference value indicates thefluctuation of the track width. As the fluctuation width of thedifference values becomes wider, the fluctuation of the track spaceincreases, in other words, areas where the track width is narrower aregenerated. When vibration is applied from the outside and thepositioning accuracy deteriorates, this RRO determines the width wherean over-write on the recording area of the data of the adjacent trackoccurs. In other words, suppressing RRO contributes to improvingresistance to external vibration.

RPE indicates the displacement from the positioning target. If controlis being performed only to follow-up RRO, RPE indicates a deviation fromRRO. In ordinary positioning control, RPE is the management target. Forexample, if RPE is contained in a plus/minus 15% range from the trackwidth, or if this status continues for a predetermined number ofsamples, data recording is enabled, or it is judged whether seek controlcompleted (stabilization completed). In other words, suppressing RPEcontributes to improving the seek response time.

RPE+RRO indicates a locus of an actuator in a status where no vibrationis applied from the outside. That is, this indicates a data recordingposition when vibration from the outside is zero. As this shows,suppressing RPE+RRO contributes to improving the positioning accuracyand error rate of recording/regenerating data in ordinary operatingstatus where external vibration is low.

In FIG. 42 and FIG. 43 the actual position ‘y’ and the position error‘e’ can be expressed by the following relational expression (1), usingthe target position ‘r’, RRO, NRRO, the transfer function of the controlsystem C (z), and the transfer function of the plant (actuator in thecase of a magnetic disk device) P (z).

$\begin{matrix}{{y = {{\frac{{C(z)} \cdot {P(z)}}{1 + {{C(z)} \cdot {P(z)}}}r} + {\frac{1}{1 + {{C(z)} \cdot {P(z)}}}{RRO}} + {\frac{1}{1 + {{C(z)} \cdot {P(z)}}}{NRRO}}}}{e = {y - r}}} & (1)\end{matrix}$

Now the status during track follow-up, when the target position ‘r’ isalways the same and no vibration is applied from the outside, will beconsidered. The term of the target position ‘r’ at the right hand sidein the expression for ‘y’, shown in expression (1), is a constant value,and is equal to the input (target position) ‘r’. Therefore expression(2) of the position error ‘e’ in the track follow-up status is obtained.

$\begin{matrix}{e = {{\frac{1}{1 + {{C(z)} \cdot {P(z)}}}{RRO}} + {\frac{1}{1 + {{C(z)} \cdot {P(z)}}}{NRRO}}}} & (2)\end{matrix}$

Note that ‘e’ in this status is also the sum of RPE and NRPE. ThereforeRRO and NRRO and RPE and NRPE are expressed in the following relationalexpressions (3). In these expressions, 1/(1+C(z)·P(z)) is generallycalled the “sensitivity function”.

$\begin{matrix}{{{RPE} = {\frac{1}{1 + {{C(z)} \cdot {P(z)}}}{RRO}}}{{NRPE} = {\frac{1}{1 + {{C(z)} \cdot {P(z)}}}{NRRO}}}} & (3)\end{matrix}$

In this way, there is a characteristic difference for the amount of thesensitivity function between RPE and RRO. In other words, there is adifference depending on the frequency. This means that even if RRO canbe suppressed, the same suppression rate cannot always be implementedfor RPE. And even if RRO can be suppressed 50%, RPE may be suppressedonly 20%. The difference in frequency characteristics must beconsidered.

There are two types of methods to suppress RRO, that is, a method forthe actuator not to follow-up RRO, as shown in FIG. 42, and a method forthe actuator to follow-up RRO, as shown in FIG. 43. Both of thesemethods have actually been applied to disk devices. A method of usingboth of these methods is also in use. For example, the actuator followsup the low frequency area and does not follow-up in the high frequencyarea.

FIG. 42 shows the method for the actuator not to follow up RRO. Acorrection table 100 for storing values, called a “RroTable” is createdin advance. And when the positioning control of the disk device isperformed, the RroTable of the correction table 100 is subtracted fromthe position error ‘e’, and the result is used for the controller C(z).In other words, the controller C(z) calculates the control amount fromthe position error from which RRO is removed. These RroTable values maybe different depending on the head, track, read position or writeposition, or may be the same for each head or each zone formed by aplurality of tracks.

One of the RroTable generation methods that has been proposed is amethod of determining RRO by computing the observing position. Anexample of this computation method is using a discrete Fourier transform(DFT) (e.g. Japanese Patent Application Laid-Open No. H 11-126444). AsFIG. 42 shows, the positional locus, that is RroTable of the correctiontable 100, is generated from the position error ‘e’, and RPE included in‘e’ is removed. The position error ‘e’ at this time is expressed by thefollowing expression (4). According to this expression (4), the actuatoroperates not to follow-up RRO.

$\begin{matrix}\begin{matrix}{e = {\frac{1}{1 + {{C(z)} \cdot {P(z)}}}\left( {{RRO} + {NRRO} - {RroTable}} \right)}} \\{= {{RPE} + {NRPE} - {\frac{1}{1 + {{C(z)} \cdot {P(z)}}}{RroTable}}}}\end{matrix} & (4)\end{matrix}$

Therefore to remove RPE from the position error ‘e’, a RroTable isgenerated so as to satisfy the following expression (5).RroTable=(1+C(z)·P(z))RPE   (5)

In other words, as FIG. 42 shows, RPE is acquired from the positionerror ‘e’ by the acquisition block 110, and the RroTable value isdetermined from the acquired RPE through the reverse characteristics ofthe sensitivity function by the RRO calculation block 112. To determineaverage values of a plurality of cycles of the disk, the addition block114 adds the RroTable value of each cycle of the disk.

In the case of the method for the actuator to follow-up RRO, on theother hand, a correction table 118 for storing a value of URroTable iscreated in advance. And during the positioning control of the diskdevice, the URroTable value of the correction table 118 is added when adrive signal is supplied from the control system C(z) to the plant P(z).This URroTable value as well may be different depending on the head,track and read position/write position, or may have a value for eachhead and for each zone which is comprised of a plurality of tracks. Eachhead may have a URroTable value regardless the track.

For this URroTable generation method as well, some methods have beenproposed, such as a method of computing the position error ‘e’ anddetermining a signal that follows up RRO. Examples of this computationmethod are a method using repeat control and a method of using adiscrete Fourier transform (e.g. see Japanese Patent ApplicationLaid-Open No. H 11-126444).

As FIG. 43 shows, the URroTable value is generated from the positionerror ‘e’, and RPE included in ‘e’ is removed. As mentioned above, theactuator operates so as to follow-up RRO and the position error ‘e’satisfies the following relational expression (6) in a track followingstatus where external vibration is not applied.

$\begin{matrix}\begin{matrix}{e = {{\frac{1}{1 + {{C(z)} \cdot {P(z)}}}\left( {{RRO} + {NRRO}} \right)} + {\frac{P(z)}{1 + {{C(z)} \cdot {P(z)}}}{URroTable}}}} \\{= {{RPE} + {NRPE} + {\frac{P(z)}{1 + {{C(z)} \cdot {P(z)}}}{URroTable}}}}\end{matrix} & (6)\end{matrix}$

Therefore in order to remove RPE from the position error ‘e’, aURroTable value is generated so as to satisfy the following expression(7). Expression (7) indicates that the URroTable value is determinedfrom RPE through the transfer function that has a reverse characteristicof the sensitivity function and the reverse characteristic of the plant.

$\begin{matrix}{{URroTable} = {{- \frac{1 + {C{(z) \cdot {P(z)}}}}{P(z)}}{RPE}}} & (7)\end{matrix}$

In other words, as FIG. 43 shows, RPE is acquired from the positionerror ‘e’ by the acquisition block 110, and the URroTable value isdetermined from the acquired RPE through the reverse characteristic ofthe sensitivity function and the reverse characteristic of the plant bythe RRO calculation block 112. If an average value of a plurality ofcycles of the disk is determined, the URroTable value of each cycle ofthe disk is added by the addition block 114.

As described above, a method of determining the correction tableRroTable or URroTable from the observed RPE is to convert through such atransfer function as (1+C(z)·P(z)) or−(1+C(z)·P(z))/P(z). For thisconversion method, a method of determining the frequency characteristicbetween RPE and Rro or URro in advance and using a discrete Fouriertransform (DFT) is best to determine waveforms most accurately.

A problem of generating the waveform of RroTable and URroTable is noise,particularly the asynchronous component in the position disturbance:NRRO. The NRRO is observed as NRPE during positioning control. Awaveform is determined using position signals regardless whether theactuator follows up the RRO or not, but the problem occurs when NRPE ismost obviously large compared with RPE.

When the NRPE is “0”, RPE can be determined simply by observing onecycle of position signals. Therefore it is easy to generate a RroTableor URroTable for the actuator to follow-up RRO completely, or not tofollow-up with RRO completely. However in reality the magnitude of RPEand NRPE are about the same, and a method of considering the error ofNRPE during RPE measurement is required.

A method of decreasing the influence of NRPE is a method of averagingthe position error ‘e’. Position signals are measured continuously for aplurality of times of rotation cycles (e.g. 100 cycles), and an averagevalue of the measured values is determined for each servo sector. Thisaverage value is regarded as the RPE, and a correction signal for notfollowing up with RRO or for following up with RRO: a Rro or URroTablevalue, is calculated. This Rro or URroTable value is calculated assumingthat no noise is included in the observed waveforms. And this value issubstituted for each servo sector in the correction tables 100 and 108of the RroTable and URroTable.

A method of simply averaging can decrease the influence of NRPE, butcannot suppress it to “0”. Also the standards of magnitude of NRPE withrespect to RPE and the number of rotation cycles to be measured arevague. So it has been proposed to multiply the averaged position errorsignals by a gain smaller than 1: Krro or Kurro, and substitute theresult in table 100 or 118 (e.g. U.S. Pat. No. 6,437,936 B1).

According to this method, when NRPE is large, or when the number ofrotation cycles for measurement is small, Krro or Kurro is adjusted byexperiment so that RPE after correction becomes small. The gain becomescloser to “0” when NRPE is large with respect to RPE, and becomes closerto “1” if small. To solve this uncertainty of gain, the measurement andcorrection of RPE are further repeated (e.g. see U.S. Pat. No.6,437,936, B1). The case when the measurement and correction arerepeated twice for example, will be considered. By using Rro [1] or URro[1] determined by the first measurement and calculation, a correctiontable is generated using the following expression (8).RroTable[1]=Krro[1]·Rro[1]URro Table[1]=Kurro[1]·URro[1]  (8)

RPE is measured a second time in the status after positioning control isperformed using the generated correction table RroTable [1] or URroTable[1]. Then Rro [2] or URro [2] is calculated again and added to theprevious correction table according to the following expression (9).RroTable[2]=Krro[2]·Rro[2]+RroTable[1]URroTable[2]=Kurro[2]·URro[2]+URroTable [1]  (9)

Today track density is increasing along with demands for increasedstorage capacity. FIG. 44 shows the fluctuation of three adjacenttracks, where the locus of the track center differs depending on thetrack. FIG. 45 shows the locus of the top and bottom tracks viewed fromthe center track in FIG. 44, and indicates the track width of the centertrack. In this way, a highly accurate RRO correction is demanded becauseof the high density of the tracks.

In the conventional method of generating an RRO correction table:RroTable or URroTable of a disk device, a method to theoreticallydetermine an optimum value of the gain: Krro or Kurro, when Rro andURro, that is a correction value, is added to the correction table, hasnot been established. Therefore it is unavoidable that an optimum valuemust be determined by experiment based on experience.

Therefore the suppression rate of RPE after correction cannot beestimated and must be confirmed by experiment. This is a problem whenthe suppression rate is adjusted for each disk device, making itimpossible to estimate the positioning accuracy value when a new deviceis designed.

Also when the correction value is measured in the manufacturing steps ofthe disk device, it is difficult to set a standard for the RPEmeasurement time, that is the manufacturing time, required forsatisfying the specifications of the positioning accuracy. For example,according to a prior art, a more accurate RRO correction table can becreated as the measurement time becomes longer (e.g. several hours), tosatisfy the specifications of the positioning accuracy, but as themeasurement time becomes longer, the ratio of the correction tablecreation time in the manufacturing steps becomes longer, which isinappropriate for manufacturing large quantities of disk devices.

Also when gain is determined by experiment, the frequency characteristicof the position error is not considered, so it is difficult toeffectively suppress RPE after correction, which may drop the follow-upaccuracy of the disk device.

SUMMARY OF THE INVENTION

With the foregoing in view, it is an object of the present invention toprovide a method of determining the gain when one of the correctionvalues, Rro or URro, is added to the correction table not based onexperiment but theoretically so as to create a correction table thatsatisfies the specifications of the positioning accuracy in a shortertime, and a head positioning control method and a disk device thereof.

It is another object of the present invention to provide a method ofoptimizing the gain when one of the correction values, Rro or URro, isadded to the correction table, so as to create a correction table thatsatisfies the specifications of the positioning accuracy in a shorttime, and a head positioning control method and a disk device thereof.

It is still another object of the present invention to provide acorrection table creation method of setting the gain, when one of thecorrection values Rro or URro is added to the correction table, at anoptimum level for each frequency, so as to effectively suppress RPEafter correction, and a head positioning control method and a diskdevice thereof.

To achieve the above objects, the correction table creation methodaccording to the present invention is a correction table creation methodfor head position control for creating correction values for correctingthe components synchronizing rotation of a disk of a disk device forcontrolling a position of a head for at least reading information of thedisk using the position signals of the disk. The method has steps of:measuring the position error components synchronizing the rotation ofthe disk from an average waveform of the position signals; correctingthe measured position error components using an adjusted gain based on aratio of the magnitude between components synchronizing the rotation ofthe disk and components not synchronizing the rotation of the disk inthe position signals; and storing the corrected position errorcomponents in the correction table.

The head position control method according to the present invention is ahead position control method for controlling the position of a head forat least reading information of a disk using signals acquired bycorrecting the position signals of the disk by components synchronizingrotation of the disk. The method has steps of: calculating the errorbetween a target position and a current position based on the positionsignal from the head; reading correction signals from a correction tablefor storing the correction signals acquired by measuring position errorcomponents synchronizing the rotation of the disk from an averagewaveform of the position signals and correcting the measured positionerror components using an adjusted gain based on the ratio of themagnitude between components synchronizing rotation of the disk andcomponents not synchronizing rotation of the disk in the positionsignals; and controlling the head position based on the position errorand the correction signals.

The disk device according to the present invention is a disk device has:a head for at least reading information of a disk; an actuator formoving the head to a desired position on the disk; a correction tablefor storing correction signals acquired by measuring position errorcomponents synchronizing the rotation of the disk from an averagewaveform of the position signals from the head and correcting themeasured position error components using an adjusted gain based on aratio of the magnitude between components synchronizing the rotation ofthe disk and components not synchronizing the rotation of the disk inthe position signals; and a control unit for calculating an errorbetween a target position and a current position based on the positionsignals from the head, and controlling the head position based on theposition error and the correction signals.

In the present invention, it is preferable that the correction stepfurther has a step of correcting the measured position error componentsusing an adjusted gain based on the number of measurement rotations foraveraging the position signals, the number of repeats of the correction,and the ratio of the magnitude between components synchronizing rotationof the disk and components not synchronizing rotation of the disk in theposition signals.

It is preferable that the present invention further has a step ofmeasuring the normal distribution of components synchronizing rotationof the disk and the normal distribution of components not synchronizingrotation of the disk in the position signals, and a step of calculatingthe adjusted gain based on the ratio between the normal distribution ofthe components synchronizing and the normal distribution of thecomponents not synchronizing.

In the present invention, it is preferable that the correction stepfurther has a step of correcting the measured position error componentsfor each repeat using a gain for each repeat, that is adjusted based onthe number of measurement rotations for averaging the position signals,the number of repeats of the correction, and the ratio of the magnitudebetween the components synchronizing rotation of the disk and thecomponents not synchronizing rotation of the disk in the positionsignals.

In the present invention, it is preferable that the correction stepfurther has a step of correcting the measured position error componentsfor each frequency, that is a multiple of the rotation frequency of thedisk, using the adjusted gain acquired by determining the ratio of themagnitude between the components synchronizing rotation of the disk andthe components not synchronizing rotation of the disk in the positionsignals.

In the present invention, it is preferable that in the storage step, theresidual RRO σ, that is a normal distribution of componentssynchronizing the rotation of a disk corrected by the correction valuestored in the correction table, follows the following expression (18),where the normal distribution of components synchronizing rotation ofthe disk is σRRO, the normal distribution of components notsynchronizing rotation of the disk is σNRRO, the number of measurementrotations is ‘N’, the number of repeats is ‘M’, and the gain is ‘K’.

$\begin{matrix}{\left( {{residual}\mspace{14mu}{RRO}\mspace{14mu}\sigma} \right)^{2} = {{\left( {1 - K} \right)^{2M}\sigma_{RRO}^{2}} + {{K^{2}/N}{\sum\limits_{i = 1}^{M}\;{\left( {1 - K} \right)^{2{({i - 1})}}\sigma_{NRRO}^{2}}}}}} & (18)\end{matrix}$

According to the present invention, an adjusted gain based on the ratioof the magnitude between the components synchronizing rotation of thedisk and the components not synchronizing rotation of the disk in theposition signals is used, so the gain to minimize RRO after correctioncan be theoretically determined using an expression for determining RROafter correction. Therefore the gain can be determined without dependingon experiment. Also the value of RRO after correction can be guaranteed,and the manufacturing time and device specifications can be determined.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram depicting a configuration of an embodiment of thedisk device according to the present invention;

FIG. 2 is a diagram depicting the arrangement of servo signals of thedisk in FIG. 1;

FIG. 3 is a diagram depicting the configuration of the servo signal inFIG. 2;

FIG. 4 is a waveform diagram of reading the servo signal in FIG. 3;

FIG. 5 is a diagram depicting the head control sequence in FIG. 1;

FIG. 6 is a block diagram depicting the servo control system in FIG. 1;

FIG. 7 is a block diagram depicting a servo control system having theRRO correction function according to an embodiment of the presentinvention;

FIG. 8 is a flow chart depicting the manufacturing steps of the diskdevice in FIG. 1;

FIG. 9 is a diagram depicting the evaluation function in FIG. 7;

FIG. 10 is a flow chart depicting the addition gain measurementprocessing in FIG. 7;

FIG. 11 is a flow chart depicting the RRO measurement processing in FIG.10;

FIG. 12 is a flow chart depicting the NRRO measurement processing inFIG. 10;

FIG. 13 is a flow chart depicting the RroTable creation processing inFIG. 7;

FIG. 14 is a flow chart depicting another RroTable correction processingin FIG. 7;

FIG. 15 are graphs depicting the first embodiment using the RroTable inFIG. 7;

FIG. 16 are graphs depicting the second embodiment using the RroTable inFIG. 7;

FIG. 17 are graphs depicting the third embodiment using the RroTable inFIG. 7;

FIG. 18 are graphs depicting the fourth embodiment using the RroTable inFIG. 7;

FIG. 19 is a block diagram depicting a servo control system having theRRO correction function according to another embodiment of the presentinvention;

FIG. 20 is a block diagram depicting a servo control system having theRRO correction function according to still another embodiment of thepresent invention;

FIG. 21 is a block diagram depicting a servo system having the URROcorrection function according to an embodiment of the present invention;

FIG. 22 is a diagram depicting the evaluation function of the URROcorrection in FIG. 21;

FIG. 23 is a block diagram depicting a servo control system having theURRO correction function according to another embodiment of the presentinvention;

FIG. 24 is a block diagram depicting a servo control system having theURRO correction function according to still another embodiment of thepresent invention;

FIG. 25 is a flow chart depicting the addition gain measurementprocessing for each RRO degree in FIG. 7;

FIG. 26 is a frequency characteristic diagram of FFT for measuring theaddition gain in FIG. 25;

FIG. 27 is a graph depicting the NRRO measurement processing in FIG. 25;

FIG. 28 is a graph depicting the RRO measurement processing in FIG. 25;

FIG. 29 is a graph depicting the RRO and NRRO in FIG. 27 and FIG. 28;

FIG. 30 is a graph depicting the optimum gain and residual RRO in FIG.25;

FIG. 31 is a diagram depicting the RPE correction operation with theoptimum gain in FIG. 25;

FIG. 32 is a table showing an example of the addition gain for each RROdegree in FIG. 25;

FIG. 33 is a graph depicting RPE before correction in FIG. 25;

FIG. 34 is a graph depicting RPE after correction in FIG. 25;

FIG. 35 is a flow chart depicting RroTable creation processing when thetrack correction shown in FIG. 7 exists;

FIG. 36 is a diagram depicting the zone division in FIG. 35;

FIG. 37 is a table showing the RroTable in FIG. 35;

FIG. 38 is a diagram depicting the servo track writing method using theRRO correction table in FIG. 7;

FIG. 39 is another diagram depicting the servo track writing methodusing the RRO correction table in FIG. 7;

FIG. 40 is a flow chart depicting the servo track rewriting method usingthe RRO correction table in FIG. 7;

FIG. 41 is a diagram depicting the storage location of the RROcorrection table in FIG. 7;

FIG. 42 is a block diagram depicting the servo control system using aconventional RRO correction table;

FIG. 43 is a block diagram depicting the servo control system using aconventional URRO correction table;

FIG. 44 is a graph depicting the track fluctuation according to aconventional RRO correction table; and

FIG. 45 is an enlarged view of the adjacent tracks in FIG. 44.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described in thesequence of disk device, optimum gain determination method for creatingan RRO correction table, an RRO correction table creation method,another RRO correction table creation method, a URRO creation tablecreation method, another RRO correction table creation methodconsidering the frequency characteristics, another RRO correction tablecreation method considering correlation, a servo track writing methodusing a RRO correction table, and other embodiments. The presentinvention, however, is not limited to the following embodiments.

Disk Device

FIG. 1 is a diagram depicting a configuration of a disk storage deviceaccording to an embodiment of the present invention, FIG. 2 is a diagramdepicting the arrangement of the position signals of the magnetic diskin FIG. 1, FIG. 3 is a diagram depicting the configuration of theposition signals of the magnetic disk in FIG. 1 and FIG. 2, FIG. 4 is awaveform diagram depicting the reading of the position signal in FIG. 3,FIG. 5 is a diagram depicting the head position control in FIG. 1, andFIG. 6 is a block diagram depicting the servo control system with theconfiguration in FIG. 1.

FIG. 1 to FIG. 6 show a magnetic disk device as the disk storage device.As FIG. 1 shows, the magnetic disk 4, which is a magnetic storagemedium, is installed at the rotation axis 2 of the spindle motor 5. Thespindle motor 5 rotates the magnetic disk 4. The actuator (VCM: VoiceCoil Motor) 1 comprises a magnetic head 3 at the top, and moves themagnetic head 3 in the radius direction of the magnetic disk 4.

The actuator 1 is comprised of a voice coil motor (VCM) that rotatesaround the rotation axis. In FIG. 1, two magnetic disks 4 are installedin the magnetic disk device, and four magnetic heads 3 aresimultaneously driven by the same actuator 1. The magnetic head 3 iscomprised of a read element and a write element. The magnetic head 3 isconstructed by layering read elements, including a magneto-resistance(MR) element, on a slider, and layering write elements, including awrite coil, thereon.

The position detection circuit 7 converts the position signals (analogsignals) read by the magnetic head 3 into digital signals. Theread/write (R/W) circuit 10 controls the reading and writing of themagnetic head 3. The spindle motor (SPM) drive circuit 8 drives thespindle motor 5. The voice coil motor (VCM) drive circuit 6 suppliesdrive current to the voice coil motor (VCM) 1, and drives the VCM 1.

The microcontroller (MCU) 14 detects (demodulates) the current positionusing the digital position signal from the position detection circuit 7,and calculates the VCM drive instruction value according to the errorbetween the detected current position and the target position. In otherwords, position demodulation and servo control are performed. The readonly memory (ROM) 13 stores the control programs of the MCU 14. Therandom access memory (RAM) 12 stores data required for the processing ofthe MCU 14.

The hard disk controller (HDC) 11 judges the position of the head on atrack based on the sector number of the servo signal, andrecords/regenerates data. The random access memory (RAM) 15 is used as abuffer memory, and temporarily stores read data and write data. The HDC11 communicates with the host via such an interface IF as ATA and SCSI.The bus 9 connects them.

As FIG. 2 shows, the servo signals (position signals) are arranged oneach track in the circumference direction at an equal interval, from theouter track to the inner track. Each track is comprised of a pluralityof sectors, and the solid line 16 in FIG. 2 shows the recorded positionsof the servo signals. As FIG. 3 shows, a position signal is comprised ofa servo mark ServoMark, track number GrayCode, index Index, and offsetinformation (servo burst) PosA, PosB, PosC and PosD. The dotted line inFIG. 3 shows the track center.

FIG. 4 is a signal waveform diagram when the position signal in FIG. 3is read by the head 3. The position of the magnetic head 3 in the radiusdirection is detected by using the track number GrayCode and offsetinformation PosA, PosB, PosC and PosD of the signal waveform shown inFIG. 4. Also based on the index signal Index, the position of themagnetic head 3 in the circumference direction is known.

For example, the sector number when the index signal is detected is setto No. 0, and this number is incremented each time the servo signal isdetected, and the sector number of each sector of a track is acquired.The sector number of the servo signal becomes a reference when data isrecorded and regenerated. There is one index signal on a track. Thesector number may be set instead of or along with the index signal.

FIG. 5 is an example of seek control of the actuator performed by theMCU 14 in FIG. 1. Through the position detection circuit 7 in FIG. 1,the MCU 14 confirms the position of the actuator 1, performs servocomputation, and supplies an appropriate current to the VCM 1. FIG. 5shows the transition of control from the start of seeking, when the head3 is moved from a track position to the target track position, thecurrent of the actuator 1, the speed of the actuator 1 (head 3), and theposition of the actuator 1 (head 3).

In other words, in seek control, the head can be moved to the targetposition by coarse control, settlement control and following control.Coarse control is basically speed control, and settlement control andfollowing control are basically position control, where the currentposition of the head must be detected for both. Transition fromsettlement control to following control, that is the completion of seekcontrol, is judged based on RPE. Whether data can be recorded andregenerated during following control can also be judged based on RPE.

To confirm these positions, servo signals are recorded on the magneticdisk in advance, as shown in FIG. 2 to FIG. 4. In other words, as FIG. 3shows, a servo mark to indicate the start position of the servo signal,a gray code to indicate the track number, an index signal, and signalsPosA–PosD to indicate offset, are recorded. This servo signal is read bythe magnetic head 3, and the position detection circuit 7 converts thisservo signal into a digital value.

The MCU 14 performs computation of the digital servo control systemshown in FIG. 6. In other words, the error ‘e’ between the targetposition ‘r’ and the current position ‘y’ is determined by thecomputation block 22, and the controller 20 performs controlcomputation, calculates the control amount and drives the VCM 1, that isthe plant 21. For the position of the plant 21, the current position ‘y’is acquired by demodulating the servo signal from the magnetic head 3.The difference between the current position ‘y’ and the target position‘r’ becomes the position error ‘e’.

In FIG. 6, the components synchronizing rotation of the spindle motor 5and the components not synchronizing are denoted as RRO, NRRO, RPE andNRPE as the disturbance applied to the control system. RRO (RepeatableRun Out) are the components of positional disturbance synchronizingrotation. NRRO (Non-Repeatable Run Out) are components of positionaldisturbance not synchronizing rotation. In the present invention, alldisturbances are considered in position units. For example, the winddisturbance applied to the actuator 1 is expressed in accelerationunits, but this is converted into position units here. RPE (RepeatablePosition Error) are components synchronizing rotation included in theposition error ‘e’ when positioning control is performed. NRPE(Non-Repeatable Position Error) are components not synchronizingrotation included in the position error ‘e’ when positioning control isperformed. RRO and RPE show different values depending on the servosector.

If this RPE can be observed without errors, the RroTable or URroTablecan be generated correctly. But in practical terms, RPE must bedetermined from the observing position ‘y’, and the observing position‘y’ includes not only RPE but NRPE as well. This NRPE becomes an errorwhen REP is observed. Therefore in order to minimize the influence ofNRPE, a method of increasing the number of times of measurement isgenerally used.

In other words, the average value of the observing positions ‘y’measured when using a plurality of times of sampling is determined inorder to determine RPE, but measurement time is limited, and theinfluence of NRPE therefore cannot be completely suppressed to zero. Inparticular, when RPE is measured in an extremely short measurement time,such as one rotation or two rotations, a method for decreasing theinfluence of NRPE included as an error has been demanded. Now a methodfor decreasing the influence of error required for generating RroTablewill be generated.

Optimum Gain Determination Method for Creating RRO Correction Table

FIG. 7 is a block diagram depicting the first embodiment of the headpositioning control system of the present invention, FIG. 8 is a flowchart depicting the manufacturing steps of the disk device of thepresent invention, FIG. 9 is a diagram depicting the residual RRO forcreating RroTable, FIG. 10 is a flow chart depicting the RRO gainoptimum value calculation processing using the residual RRO in FIG. 9,FIG. 11 is a flow chart depicting the RRO measurement processing, andFIG. 12 is a flow chart depicting the NRRO measurement processing inFIG. 10.

FIG. 7 is a block diagram for the case when the optimum valuecalculation and the correction table creation are performed on a singledisk device unit, and composing elements the same as those in FIG. 6 aredenoted with the same reference numerals. In other words, the error ‘e’between the target position ‘r’ and the current (observing) position ‘y’is determined by the computation block 22, the controller 20 performscontrol computation, calculates control amount and drives the VCM 1,that is the plant 21. For the position of the plant 21, servo signalsare demodulated from the magnetic head 3, and the current position ‘y’is acquired. The difference between the current position ‘y’ and thetarget position ‘r’ becomes the position error ‘e’. As disturbances tobe applied to this control system, components synchronizing rotation ofthe spindle motor 5 and components not synchronizing are shown as RRO,NRRO, RPE and NRPE.

The RPE acquisition block 26 acquires RPE from the position error ‘e’for each sector, as described in FIG. 13. The positioning accuracymeasurement block 24 measures the positioning accuracy from the positionerror ‘e’, as described later in FIG. 10 to FIG. 12. The optimizationcalculation block 25 calculates the optimum gain when the number ofrepeats is M, as described in FIG. 10. The waveform calculation block 27calculates the RRO waveform by multiplying RPE acquired by the RPEacquisition block 26 by the optimum gain as described later in FIG. 13.The RRO table 29 stores the RRO waveform. The addition block 28 adds theRRO waveform for the number of repeats, and updates the table 29, asdescribed later in FIG. 13.

After creating the RRO table 29, the target position ‘r’ and the Rrotable value of the correction table 29 are subtracted from the observingposition ‘y’, and the position error ‘e’ is generated by the computationblock 22 in magnetic disk device operating status (particularly in thefollowing status). By this, RRO correction is performed for the input‘e’ to the controller 20.

Before describing the optimum value (gain) calculation and thecorrection table calculation, the manufacturing steps of the magneticdisk device will be described with reference to FIG. 8. First a disk onwhich servo signals have been recorded and other mechanical components(e.g. VCM, magnetic head and spindle motor in FIG. 1) are assembled.Then an electronic board on which various circuits (e.g. MCU, HDC inFIG. 1) are mounted is installed on the disk device. Then the respectivedifference of the disk device, regarding the output of the magnetic headand the current value of VCM, is calculated.

Then the above-mentioned RRO correction table is created using themagnetic disk device after calibration. Then using the RRO correctiontable, VCM 1 is driven and the positioning accuracy of the magnetic headis measured and confirmed for each track. A track for which a desiredpositioning accuracy cannot be acquired is not used, and an alternativetrack is set. Also the data recording/regeneration test is performed tocheck if a desired recording/regeneration is possible. And the confirmedmagnetic disk device is shipped out to the market.

Now the evaluation function for calculating the optimum value of thegain will be described. First RroTable (correction table) is generated,and a specific sector is considered, for residual RRO after RROcorrection is executed, for positioning control. In other words, as FIG.9 shows, the residual RRO is the result of subtracting the RROcorrection value of RroTable 29 from the actual RRO.

Here it is assumed that the value of the sum of RRO+NRRO can be observedby applying a discrete Fourier transform (DFT) to the observing position‘y’. This waveform of RRO+NRRO is observed continuously for N rotations,and the average value of each sector is measured. It is assumed that RROof this sector is RO. It is also assumed that the value of NRRO at eachmeasurement changes as n11, n12, . . . , n1N. At this time, the waveformof RRO+NRRO after averaging for N rotations, that is the RRO estimatedvalue, is given by the following expression (10).

$\begin{matrix}{R_{0} + {{1/N}{\sum\limits_{i = 1}^{N}\; n_{1i}}}} & (10)\end{matrix}$

This value is multiplied by the gain K, and the result is substituted inthe RRO correction table RroTable 29. (The RRO correction table is “0”because this is the first measurement.) Then positioning control isperformed using the RRO correction table, and the residual RRO is givenby the expression (11).

$\begin{matrix}{R_{1} = {{R_{0} - {K\left\{ {R_{0} + {{1/N}{\sum\limits_{i = 1}^{N}\; n_{1i}}}} \right\}}} = {{\left( {1 - K} \right)R_{0}} - {{K/N}{\sum\limits_{i = 1}^{.N}\; n_{1i}}}}}} & (11)\end{matrix}$

In the same way, the second measurement is performed where the value ismultiplied by the addition gain K, and the result is added to the RROcorrection table 29, and positioning control is performed using-the RROcorrection table, then the residual RRO: R2, is given by the expression(12).

$\begin{matrix}\begin{matrix}{R_{2} = {R_{1} - {K\left\{ {R_{1} + {{1/N}{\sum\limits_{i = 1}^{M}\; n_{2i}}}} \right\}}}} \\{= {{\left( {1 - K} \right)^{2}R_{0}} - {{K/N}\left\{ {{\left( {1 - K} \right){\sum\limits_{i = 1}^{N}\; n_{1i}}} + {\sum\limits_{i = 1}^{N}\; n_{2i}}} \right\}}}}\end{matrix} & (12)\end{matrix}$

If this is repeated sequentially, then the residual RRO: RM, after Mtimes of correction is given by the following expression (13). In thefollowing expression however, the suffix of NRRO “i” is replaced with“j”.

$\begin{matrix}{R_{M} = {{\left( {1 - K} \right)^{M}R_{0}} - {{K/N}{\sum\limits_{i = 1}^{M}\;\left\{ {\left( {1 - K} \right)^{i - 1}{\sum\limits_{j = 1}^{N}\; n_{ij}}} \right\}}}}} & (13)\end{matrix}$

RO, which is the original RRO of each sector, is assumed to presentnormal distribution if it is observed at many tracks. It is generallyknown that NRRO also presents normal distribution. And RRO and NRRO arenot correlated. Therefore RRO and NRRO can be considered independently.

In other words, the components created by RRO in the first term at theright hand side in expression (13), and the components caused by NRRO inthe second term, can be handled separately. For variance when theresidual RRO is determined at many points, the standard deviationscorresponding to the first term of expression (13) and the standarddeviation corresponding to the second term thereof are determinedindependently, the sum of the squares of the respective results becomesthe variance.

First for the RRO of the first term, Nm number of RROs at each sectorare measured at many tracks, and if the values are R1, R2, . . . , RNm,the standard deviation σRRO of the RRO is determined by the followingexpression (14).

$\begin{matrix}{\sigma_{RRO}^{2} = {\sum\limits_{i = 1}^{Nm}\;{{Ri}^{2}/\left( {{Nm} - 1} \right)}}} & (14)\end{matrix}$

The components created by RRO in the residual RRO after correctionfollow the first term at the right hand side of expression (13), so RROat many points is regarded as R1, R2, . . . , RNm instead of RO in thefirst term at the right hand side, and this is substituted in expression(14), then the variance of the components created by RRO in the residualRRO: RM (square of standard deviation σRRO) can be expressed by thefollowing expression (15).

$\begin{matrix}\begin{matrix}{{\sum\limits_{i = 1}^{Nm}\;{\left\{ {\left( {1 - K} \right)^{M}{Ri}} \right\}^{2}/\left( {{Nm} - 1} \right)}} = {\left( {1 - K} \right)^{2M}{\sum\limits_{i = 1}^{Nm}{{Ri}^{2}/\left( {{Nm} - 1} \right)}}}} \\{= {\left( {1 - K} \right)^{2M}\sigma_{RRO}^{2}}}\end{matrix} & (15)\end{matrix}$

Then for NRRO, the standard deviation caused by NRRO is assumed to beσNRRO. The distribution of nij in the second term at the right hand sidein expression (13) follows this standard deviation σNRRO. In otherwords, if the sum of NRRO for N samples is expressed by the standarddeviation σNRRO, that is an expected value of the sum, then the resultbecomes the following expression (16).

$\begin{matrix}{{\sum\limits_{i = 1}^{N}n_{ij}} = {\left( {\sum\limits_{i = 1}^{N}\sigma_{NRRO}^{2}} \right)^{0.5} = {\sqrt{N}\sigma_{NRRO}}}} & (16)\end{matrix}$

Therefore if the variance of the components caused by NRRO in the secondterm at the right hand side in expression (13) is expressed using σNRRO,expression (16) is substituted in the second term at the right hand sideof expression (13), and the result is squared, then this result can beexpressed by the following expression (17).

$\begin{matrix}{{{K^{2}/N^{2}}{\sum\limits_{i = 1}^{M}\left\{ {\left( {1 - K} \right)^{2{({i - 1})}}\left( {\sqrt{N}\sigma_{NRRO}} \right)^{2}} \right\}}} = {{K^{2}/N}{\sum\limits_{i = 1}^{M}{\left( {1 - K} \right)^{2{({i - 1})}}\sigma_{NRRO}^{2}}}}} & (17)\end{matrix}$

Therefore the variance of residual RRO after correction (square of σ)can be expressed by expression (18), using expression (15) andexpression (17). This becomes an evaluation expression for calculatingthe effect of RRO correction. Under given conditions, the variables canbe adjusted so that the value of expression (18) becomes the minimum. Ifthis expression is used, a combination of optimum variables: N (numberof samples), M (number of repeats of measurement and correction) and K(addition gain), can be determined according to the σ ratio of RRO andNRRO.

$\begin{matrix}{\left( {{residual}\mspace{14mu}{RRO}\;\sigma} \right)^{2} = {{\left( {1 - K} \right)^{2M}\sigma_{RRO}^{2}} + {{K^{2}/N}{\sum\limits_{i = 1}^{M}{\left( {1 - K} \right)^{2{({i - 1})}}\sigma_{NRRO}^{2}}}}}} & (18)\end{matrix}$

Then an algebraic solution of the optimum conditions to minimize theresidual RRO is determined from expression (18). First the case when thenumber of repeats M is “1” is considered. In expression (18), if thevalue of the number of repeats M is “1”, then expression (18) becomesthe following expression (19).(residualRROσ)²=(1−K)²σ_(RRO) ²+(K ² /N)σ_(NRRO) ²   (19)

If the ratio of the respective a of RRO and NRRO before correction is‘r’ and is substituted in expression (19), then the standard deviation r[1] of the residual RRO, normalized using the ratio ‘r’, can beexpressed as the following expression (20).r ²=σ_(RRO) ²/σ_(NRRO) ²Variance of normalized residual RRO=r[1]²=(1−K)² r ² +K ² /N   (20)

In order to determine the addition gain K to minimize the residual RRO,the conditions, under which the value when expression (20) isdifferentiated with K becomes “0”, are determined. In other words, ifthe differential value is “0”, then the residual RRO becomes theminimum. Therefore the addition gain K, that minimizes the residual RRO,can be acquired by the following expression (21).

$\begin{matrix}\begin{matrix}{{\frac{\partial}{\partial K}{r\lbrack 1\rbrack}^{2}} = {{{{- 2}\left( {1 - K} \right)r^{2}} + {2{K/N}}} = 0}} \\{\left. \rightarrow K \right. = \frac{{Nr}^{2}}{{Nr}^{2} + 1}}\end{matrix} & (21)\end{matrix}$

At this time the standard deviation r [1] of the normalized residual RRO(normalized residual RRO after first correction) of the expression (20)is acquired by the following expression (22) substituting expression(21) in expression (20).

$\begin{matrix}\begin{matrix}{{r\lbrack 1\rbrack}^{2} = {{\left( {1 - \frac{{Nr}^{2}}{{Nr}^{2} + 1}} \right)^{2}r^{2}} + {\left( \frac{{Nr}^{2}}{{Nr}^{2} + 1} \right)^{2}\frac{1}{N}}}} \\{= {{\frac{r^{2}}{\left( {{Nr}^{2} + 1} \right)^{2}} + \frac{{Nr}^{4}}{\left( {{Nr}^{2} + 1} \right)^{2}}} = \frac{r^{2}}{{Nr}^{2} + 1}}}\end{matrix} & (22)\end{matrix}$

As a consequence, for the optimum gain K, the variance of the normalizedresidual RRO, the variance of the residual RRO, the ratio of theresidual RRO to the original RRO, which indicates the positioningaccuracy, and the RRO reduction ratio, the relational expressions shownin the following (23), can be derived. By this, if N (number ofsamples), σRRO (standard deviation of RRO) and σNRRO (standard deviationof NRRO) are given, then the gain K to minimize the residual RRO isuniquely determined.

$\begin{matrix}{{{{Optimum}\mspace{14mu}{gain}\text{:}\mspace{14mu} K} = \frac{{Nr}^{2}}{{Nr}^{2} + 1}}{{{Variance}\mspace{14mu}{of}\mspace{14mu}{normalized}\mspace{14mu}{residual}\mspace{14mu}{RRO}\;\text{:}\mspace{11mu}\;{r\lbrack 1\rbrack}^{2}} = {\frac{r^{2}}{{Nr}^{2} + 1} = \frac{K}{N}}}\begin{matrix}{{{Variance}\mspace{14mu}{of}\mspace{14mu}{residual}\mspace{14mu}{RRO}\text{:}\mspace{14mu}{r\lbrack 1\rbrack}^{2}\sigma_{NRRO}^{2}} = {\frac{r^{2}}{{NR}^{2} + 1}\sigma_{NRRO}^{2}}} \\{= {\frac{K}{N}\sigma_{NRRO}^{2}}}\end{matrix}{{{Ratio}\mspace{14mu}{of}\mspace{14mu}{residual}\mspace{14mu}{RRO}\mspace{14mu}{to}\mspace{14mu}{original}\mspace{14mu}{RRO}\text{:}\mspace{14mu}\sqrt{\frac{1}{{Nr}^{2} + 1}}} = \sqrt{\frac{K}{{Nr}^{2}}}}{{{{RRO}\mspace{14mu}{reduction}\mspace{14mu}{rate}\text{:}\mspace{14mu} 1} - \sqrt{\frac{1}{{Nr}^{2} + 1}}} = {1 - \sqrt{\frac{K}{{Nr}^{2}}}}}} & (23)\end{matrix}$

The above expressions exist when the number of repeats M of measurementand correction is “1”, and the optimum addition gain K [k] and thenormalized residual RRO: r [M] when the number of repeats M is 2 or moreare determined. From expression (21) and expression (22), the followingexpression (24) is acquired. Here K [1] and K [2] are gains withdifferent values. In other words, each time one measurement andcorrection is repeated, the optimum addition gain K can be set for eachtime, changing the addition gain K value.

$\begin{matrix}{{{K\lbrack M\rbrack} = \frac{{Nr}^{2}}{{MNr}^{2} + 1}}{{r\lbrack M\rbrack}^{2} = {\frac{K\lbrack M\rbrack}{N} = \frac{r^{2}}{{MNr}^{2} + 1}}}} & (24)\end{matrix}$

Therefore when the number of repeats M is an arbitrary number, therelational expressions shown in the following (25) are acquired, justlike expressions (23).

$\begin{matrix}{{{{Optimum}\mspace{14mu}{gain}\mspace{14mu}{at}\mspace{14mu}{Mth}\mspace{14mu}{repeat}\text{:}\mspace{14mu}{K\lbrack M\rbrack}} = \frac{{Nr}^{2}}{{MNr}^{2} + 1}}{{Variance}\mspace{14mu}{of}\mspace{14mu}{normalized}\mspace{14mu}{RRO}\mspace{14mu}{at}\mspace{14mu}{Mth}\mspace{14mu}{repeat}\text{:}}{{r\lbrack M\rbrack}^{2} = {\frac{K\lbrack M\rbrack}{N} = \frac{r^{2}}{{MNr}^{2} + 1}}}{{Variance}\mspace{14mu}{of}\mspace{14mu}{RRO}\mspace{14mu}{at}\mspace{14mu}{Mth}\mspace{14mu}{repeat}\text{:}}{{{r\lbrack M\rbrack}^{2}\sigma_{NRRO}^{2}} = {{\frac{K\lbrack M\rbrack}{N}\sigma_{NRRO}^{2}} = {\frac{r^{2}}{{MNr}^{2} + 1}\sigma_{NRRO}^{2}}}}{{Ratio}\mspace{14mu}{of}\mspace{14mu}{residual}\mspace{14mu}{RRO}\mspace{14mu}{to}\mspace{14mu}{original}\mspace{14mu}{RRO}\text{:}}{\sqrt{\frac{1}{{MNr}^{2} + 1}} = {{{\sqrt{\frac{K\lbrack M\rbrack}{{Nr}^{2}}}{RRO}\mspace{14mu}{reduction}\mspace{14mu}{rate}\text{:}\mspace{14mu} 1} - \sqrt{\frac{1}{{MNr}^{2} + 1}}} = {1 - \sqrt{\frac{K\lbrack M\rbrack}{{Nr}^{2}}}}}}} & (25)\end{matrix}$

With reference to FIG. 11 and FIG. 12, the optimum gain calculationprocessing is described according to FIG. 10.

(S10) Using the magnetic disk device with the configuration shown inFIG. 1, the magnetic disk 4 is rotated, and the magnetic head 3 istrack-follow controlled by the control system shown in FIG. 7 accordingto the servo information of the magnetic disk 4, and RRO and NRRO aremeasured. For the measurement of RRO, the magnetic disk is divided intoa plurality of zones in the radius direction, as shown in FIG. 11, andthe magnetic head is positioned in a representative track of each targetzone. And the positioning accuracy measurement block 24 in FIG. 7measures PES (Positioning Error Signal (error ‘e’ in FIG. 7) in eachsector of the representative track in all the target zones. Themeasurement block 24 calculates the average value of the plurality oftracks for each sector, and acquires the average value as RPE(Repeatable Position Error). As expressions (3) show, this RPE of eachsector is multiplied by the transfer function (1+CP) so as to calculatethe RRO of each sector. In the same way, for the measurement of NRRO,PES of one representative track of each sector is measured for arelatively long time, e.g. 512 rotations of the disk, as shown in FIG.12, and the average value thereof is calculated as RPE. Then for eachsector, RPE is subtracted from the measured PES, and NRPE of each sectoris calculated. The power spectrum of this calculated NRPE is calculatedby an FFT (Fast Fourier Transform), and is separated into eachfrequency. NRPE separated for each frequency is multiplied by thetransfer function (1+CP) as shown in expressions (3), and the powerspectrum of NRRO for each frequency is calculated.

(S12) Then the optimum value calculation block 25 in FIG. 7 calculatesthe standard deviation σrro of RRO from the determined RRO of eachsector according to expression (14). In the same way, the standarddeviation σnrro of NRRO is calculated from the determined NRRO of eachsector according to expression (16).

(S14) The ratio ‘r’ of the standard deviation σ is calculated from thestandard deviation σrro of RRO and the standard deviation σnrro of NRROusing expression (20), and the optimum gain K or K [M] is calculatedusing expression (21) or expression (24).

In this way, the evaluation function is determined with the residual RROafter correction as the evaluation target, and the gain to minimize theresidual RRO, that is to minimize the RRO after correction, istheoretically determined from the evaluation function. Therefore thecorrection table creation gain can be determined without depending onexperiment. Also the value of RRO after correction can be guaranteed,and the manufacturing time and device specifications can be determined.

RRO Correction Table Creation Method

FIG. 13 is a flow chart depicting the RRO correction table creationprocessing when M=1. Here it is assumed that the optimum gain K has beendetermined by the positioning accuracy measurement block 24 and theoptimum value calculation block 25 in FIG. 7 in the processing in FIG.10, and the RRO correction table 29 creation processing, by the RPEacquisition block 26 and the waveform calculation block 27 in FIG. 7will be described.

(S20) First the RroTable correction value ProTable (q) of each sector qof the correction table 29 is initialized to “0”. ‘q’ here takes a value0−(Ns−1). In other words, the number of servo sectors in one rotation isNs.

(S22) The position error PES of each sector k for all the N rotation ofthe magnetic disk 4, that is PES (k+i·Ns) is measured, and the averagevalue RPE (k) of the position error PES of each sector k is calculated.In other words, here it is assumed that the pointer of the sector is‘k’, the number of servo sectors in one rotation is Ns, and ‘i’ is thenumber of rotations (first cycle, second cycle, . . . , Nth cycle).Therefore in the expression in FIG. 13, the sum of the position error ofeach rotation of a same sector k, that is PES (k+i·Ns), is determined,and divided by the number of measurement rotations N so as to obtain theaverage.

(S24) Then DFT is performed for the RPE waveform that was observedfirst. If the number of servo sectors in one rotation is Ns, the RROdegree that must be considered at this time is 1 to (Ns/2−1) accordingto the sampling theorem. To perform DFT for the m degree of the RROfrequency, m order of coefficients of cos and sin are expressed as C(m)and S(m) respectively, and one rotation of the RPE waveform from sectorNo. 0 to No. (Ns−1) is multiplied by m order of the cos waveform and thesin waveform, and is added. In other words, expression (26) iscalculated.

$\begin{matrix}{{{C(m)} = {\sum\limits_{k = 0}^{N_{S} - 1}\left\{ {{{RPE}(k)} \cdot {\cos\left( {2\pi\; m\;{k/N_{S}}} \right)}} \right\}}}{{S(m)} = {\sum\limits_{k = 0}^{N_{S} - 1}\left\{ {{{RPE}(k)} \cdot {\sin\left( {2\pi\; m\;{k/N_{S}}} \right)}} \right\}}}{{m = 1},2,\ldots\mspace{11mu},\left( {{N_{S}/2} - 1} \right)}} & (26)\end{matrix}$

(S26) Then to determine Rro (or Urro), the transfer function ismultiplied for each RRO degree. The frequency characteristic to bemultiplied (complex number value of the m order of the RRO frequency) isdetermined in advance as a (m)+jb (m). Specifically the complex numbervalue of the m order of the frequency is determined by the transferfunction shown in expression (5) or in expression (7). By multiplyingthese characteristics, the m order of components can be expressed byexpression (27) with complex number values. That is, C2(m) and S2(m) aredetermined from C(m), S(m), a(m) and b(m).C 2(m)=C(m)a(m)−S(m)b(m)S 2(m)=C(m)b(m)+S(m)a(m)m=1,2, . . . , (N _(s)/2−1)   (27)

(S28) Then inverse DFT is performed and the waveform to be determined isacquired. The m order of computation is performed from the first orderto the (Ns/2−1)th order. When the RroTable is generated, the qth RROwaveform: RRO (q) of the sector, is determined by the followingexpression (28) (the same expression is also used for generating thelater mentioned URroTable).

$\begin{matrix}{{{{RRO}(q)} = {\sum\limits_{m = 1}^{{N_{S}/2} - 1}{\left\{ {{C\; 2(m){\cos\left( {2\pi\;{{mq}/N_{S}}} \right)}} + {S\; 2(m){\sin\left( {2\pi\;{{mq}/N_{S}}} \right)}}} \right\} \cdot \frac{2}{N_{S}}}}}{{q = 0},1,\ldots\mspace{11mu},\left( {N_{S} - 1} \right)}} & (28)\end{matrix}$

(S30) Finally the determined RRO (q) is multiplied by theabove-mentioned optimum gain K and is stored in the RroTable (q) of thecorrection table 29, and processing ends.

Now the case when the number of times of measurement and correction(repeats) M is 2 or more will be described. FIG. 14 is a flow chartdepicting the RRO correction table creation processing when M is 2 ormore. Here as well it is assumed that the optimum gain K (M) has beendetermined in the processing in FIG. 10 by the positioning accuracymeasurement block 24 and the optimum value calculation block 25 in FIG.7, and the RRO correction table 29 creation processing by the RPEacquisition block 26 and the waveform calculation block 27 in FIG. 7will be described.

(S40) The measurement and correction count value Count M is initializedto “0”.

(S42) First, just as in FIG. 13, the RRO correction value ProTable (q)of each sector q of the correction table 29 is initialed to “0”. ‘q’here is a value in a 0 to (Ns-1) range. In other words, the number ofservo sectors in one rotation is Ns.

(S44) The position error PES of each sector k of all the N rotations ofthe magnetic disk 4, that is PES (k+i·Ns), is measured, and the averagevalue RPE (k) of the position error PES of each sector k is calculated.In other words, here it is assumed that the pointer of the sector is k,the number of servo sectors in one rotation is Ns, and ‘i’ is the numberof rotations (first cycle, second cycle, . . . , Nth cycle). Thereforein the expression in FIG. 14, the sum of the position error of eachrotation of a same sector k, that is PES (k+i·Ns), is determined, and isdivided by the number of measurement rotations N so as to obtain theaverage.

(S46) Then DFT is performed for the RPE waveform that was observedfirst. If the number of servo servers in one rotation is Ns, then theRRO degree is 1 to (Ns/2−1) according to the sampling theorem. Toperform DFT for the m degree of the RRO frequency, m order ofcoefficients of cos and sin are expressed as C(m) and S(m) respectively,and one rotation of an RPE waveform from sector No. 0 to No. (Ns−1) ismultiplied by m order of cos waveform and sin waveform, and added. Inother words, the above expression (26) is calculated.

(S48) Then to determine Rro (or URro), the transfer function ismultiplied for each RRO degree. The frequency characteristic to bemultiplied (complex number value of the m order of the RRO frequency) isdetermined in advance as a (m)+jb (m). Specifically the complex numbervalue of the m order of the frequency is determined by the transferfunction shown in expression (5) or expression (7). By multiplying thesecharacteristics, the m order of components can be expressed by theabove-mentioned expression (27) with complex number values. That isC2(m) and S2(m) are determined from C(m), S(m), a(m) and b(m).

(S50) Then inverse DFT is performed, and the waveform to be determinedis acquired. A m order of computation is performed from the first orderto (Ns/2−1)th order. When the RroTable is generated, the qth RROwaveform: RRO (q) of the sector is determined by the above-mentionedexpression (28) (the same expression is also used for generating thelater mentioned URroTable).

(S52) Then the determined RRO (q) is multiplied by the above-mentionedoptimum gain K (Count M), the result is added to the RroTable (q) of thecorrection table 29, and the added value is stored. And the measurementand correction count value Count M is incremented “1”.

(S54) It is judged whether the measurement and correction count valueCount M is “M” or more. If the count value Count M does not exceed “M”,processing returns to step S44. If the count value Count M is “M” ormore, M times of measurement and correction have been completed, so thecorrection table creation processing ends.

Now examples will be described. FIG. 15 and FIG. 16 show the comparisonof the measurement result of the respective residual rate of RPE, RRO,and RPE+RRO, and the simulation of the residual rate of RRO when theabscissa is the addition gain K and when the addition gain is changed.FIG. 15 shows the experiment result (circles) and the simulation result(dotted line) when the number of rotations for averaging N=1 and thenumber of repeats M=1, and the top graph is the experiment result of theresidual rate of RPE (residual RPE/original RPE), the middle graph isthe experiment result and the simulation result of the residual rate ofRRO (residual RRO/original RRO), and the bottom graph is the experimentresult of the residual rate of RPE and RRO.

The actual disk device in FIG. 1 is used for the experiment, and thecorrection table 29 is created by the control system in FIG. 7 with eachaddition gain K shown on the abscissa, and while correcting the positionerror ‘e’ using the correction table 29 as shown in FIG. 7, the actuator1 is controlled, and the observing position ‘y’ is observed, and theresidual RPE, residual RRO and residual RPE+RRO are determined. For thesimulation, on the other hand, the RRO residual rate is calculated byexpression (23), using each addition gain K shown on the abscissa.

FIG. 16 shows the experiment result (circles) and the simulation result(dotted line) when the number of rotations for averaging N=8 and thenumber of repeats M=1, and the top graph is the experiment result of theRPE residual rate (residual RPE/original RPE), the middle graph is theexperiment result and the simulation result of the RRO residual rate(residual RRO/original RRO), and the bottom graph is the experimentresult of the residual rate of RPE+RRO. The experiment and thesimulation are the same as FIG. 15.

As FIG. 15 and FIG. 16 show, it was confirmed by experiment that theaddition gain with which the RRO residual rate is the minimum is roughlythe same for both the experiment result (circles) and the simulationresult (dotted line), in other words, experiment confirmed that thetheoretical expression (23) is correct.

FIG. 17 and FIG. 18 are graphs depicting the comparison of the RROresidual rate between the simulation result and the experiment resultwhen the optimum gains under different conditions (number of rotationsfor averaging N×number of repeats M) are set. In FIG. 17 and FIG. 18,the abscissa is the addition gain, and the dots of the RRO residualrate, under conditions where the average number of rotations foraveraging N×number of repeats M are the same, are connected by lines.FIG. 18 is a relational diagram of the RRO residual rate at the optimumgain actually measured, and just like FIG. 15 and FIG. 16, the gain thatminimizes the RRO residual rate is determined by experiment.

FIG. 17 is a relational diagram of the simulation result of the RROresidual rate with the calculated optimum gain. This is the result whenthe optimum addition gain K at each number of rotations for averagingN×number of repeats M is calculated according to expression (24), andthe RRO residual rate is simulated according to expression (25). In FIG.17, calculation was performed under the conditions of σnrro/σrro=1.15.

The characteristic of the RRO residual rate in FIG. 17 and thecharacteristic of the RRO residual rate in FIG. 18 are extremelysimilar. In other words, the experiment confirmed that the theoreticalexpression (24) is correct. In this way, the evaluation function isdetermined using the residual RRO after correction as the evaluationtarget, and using the evaluation function, the gain K and K (Count M),which minimizes the residual RRO, that is which minimizes the RRO aftercorrection, are determined by FIG. 10, and a correction table is createdaccording to FIG. 13 and FIG. 14. Therefore the correction tablecreation gain, which is the optimum for the creation time andspecifications of the device, is determined without depending onexperiment, and by this, the correction table can be created. Also thevalue of RRO after correction can be guaranteed, and the manufacturingtime and device specifications can be determined.

Another RRO Correction Table Creation Method

FIG. 19 is a block diagram depicting the RRO correction table creationsystem according to the second embodiment of the present invention. InFIG. 19, composing elements the same as FIG. 7 are denoted with the samereference numerals, and the difference from FIG. 7 is that the optimumgain calculation processing 25 (FIG. 10) is executed by an externaldevice (e.g. personal computer) 50 connected to the disk device, and theresult is set in the gain table 30 in the disk device.

If this configuration is used, the addition gain is calculated using theexternal device 50, so the load of the MCU 14 in the disk device can bedecreased, and the addition gain can be calculated at high-speed.

FIG. 20 is a block diagram depicting the RRO correction table creationsystem according to the third embodiment of the present invention. InFIG. 20, composing elements the same as FIG. 7 are denoted with the samereference numerals, and the difference from FIG. 7 is that thepositioning accuracy measurement processing 24, the optimum gaincalculation processing 25 (FIG. 10–FIG. 12), the RPE acquisitionprocessing 26 (FIG. 13), and the waveform calculation processing 27(FIG. 13) are executed by an external device (e.g. personal computer) 50connected to the disk device, and the result is set in the RROcorrection table 29 in the disk device.

When this configuration is used, the table values of the RRO correctiontable 29 are calculated, so the load of the MCU 14 of the disk devicecan be decreased further, and the table values can be calculated athigh-speed. Also the correction table creation processing program isunnecessary in the disk device after shipment of the disk device, so thetime required for loading this program onto the disk device can beeliminated.

For a plurality of disk devices in a same lot, a correction table 29 ofa representative disk device may be created in the configuration in FIG.19 or FIG. 20, and copied to other disk devices. This can decreasefurther the manufacturing time.

URRO Correction Table Creation Method

The above mentioned various expressions are on the ProTable. The issueregarding noise, however, can be discussed in the same way as for thecurrent waveforms: URroTable, as well. In other words, RroTable can beconverted into URroTable according to the later mentioned relationalexpression. The current waveform URroTable is generated so that thelocus of the actuator matches with RRO.

FIG. 21 is a block diagram depicting the case when the optimumcalculation and the URro correction table creation are performed for asingle disk device unit, where the composing elements the same as inFIG. 6 and FIG. 7 are denoted with the same reference numerals. In otherwords, the computation block 22 determines the error ‘e’ between thetarget position ‘r’ and the current (observing) position ‘y’, thecontroller 20 performs control computation and calculates the controlamount, the addition block 30 adds the URro correction values of theURro correction table 36, and drives the VCM 1, that is the plant 21.For the position of the plant 21, servo signals from the magnetic head 3are demodulated and the current position ‘y’ is acquired. The differencebetween this current position ‘y’ and the target position ‘r’ is theposition error ‘e’. As external disturbances to be applied to thiscontrol system, components synchronizing with rotation of the spindlemotor 5 and the components not synchronizing therewith are indicated asRRO, NRRO and RPE and NRPE.

As described in FIG. 13, the RPE acquisition block 26 acquires RPE fromthe position error ‘e’ for each sector. The positioning accuracymeasurement block 24 measures the positioning accuracy from the positionerror ‘e’, as described in FIG. 10 to FIG. 12. The optimum gaincalculation block 25 calculates the optimum gain with the number ofrepeats M, as described in FIG. 10. The waveform calculation block 27multiplies the RPE, which was acquired by the RPE acquisition block 26,by the optimum gain, and calculates the RPO waveform, as described inFIG. 13. The URRO table 36 stores the URRO waveform. The addition block28 adds the URRO waveform for the number of repeats, and updates thetable 36, as described in FIG. 13.

After creating the URRO table 36, the computation block 33 adds theURroTable value in the correction table 36 to the control amount of thecontroller 20, and generates the control amount ‘u’. By this, URROcorrection is performed on the output of the controller 20.

FIG. 22 is a diagram depicting the URroTable value and the residual RRO.According to the above-mentioned expression (7), a URroTable value isdetermined for RPE through the inverse characteristic of the sensitivityfunction (1+C(z)·P (z)) and the inverse characteristic of the plant(1/P(z)). Therefore the residual RRO is the actual RRO from which thevalue acquired by the block 34 through ((1+C(z)·P(z))/P(z)) as the URROcorrection value of the URroTable 36 is subtracted.

According to expression (5), the RroTable value is determined for RPEthrough the inverse characteristic of the sensitivity function(1+C(z)·P(z)), so the URroTable value is acquired by the followingexpression (29)URroTable=(−1/P (Z))·RroTable   (29)

In other words, the evaluation function is the same as expression (18)for the case of RRO, but by the waveform calculation block 27 convertingthe RroTable value into the URroTable value according to the relationalexpression of expression (29), the URro correction table 36 is acquired.

FIG. 23 is a block diagram depicting the URRO correction table creationsystem according to the second embodiment of the present invention. InFIG. 23, composing elements the same as FIG. 7 and FIG. 21 are denotedwith the same reference numerals, and the difference from FIG. 21 isthat the optimum gain calculation processing 25 (FIG. 21) is executed byan external device (e.g. personal computer) 50 connected to the diskdevice, and the result is set in the gain table 30 in the disk device.When this configuration is used, the addition gain is calculated usingthe external device 50, so the load of the MCU 14 of the disk device isdecreased, and addition gain can be calculated at high-speed.

FIG. 24 is a block diagram depicting the URRO correction table creationsystem according to the third embodiment of the present invention. InFIG. 24, the same composing elements as FIG. 7 and FIG. 21 are denotedwith the same reference numerals, and the difference from FIG. 21 isthat the positioning accuracy measurement processing 24, the optimumgain calculation processing 25 (FIG. 10–FIG. 12), the RPE acquisitionprocessing 26 (FIG. 13) and the waveform calculation processing 27 (FIG.13) are executed by an external device (e.g. personal computer) 50connected to the disk device, and the result is set in the URROcorrection table 36 in the disk device.

When this configuration is used, the table values of the URRO correctiontable 36 are calculated using the external device 50, so the load of theMCU 14 of the disk device is decreased further, and the table values canbe calculated at high-speed. Also the correction table creationprocessing program is unnecessary in the disk device after shipment ofthe disk device, so the time required for loading this program onto thedisk device can be eliminated.

For a plurality of disk devices in a same lot, a correction table 36 ofa representative disk device may be created in the configuration in FIG.23 or FIG. 24, and copied to other disk devices. This can furtherdecrease the manufacturing time.

Another RRO Correction Table Creation Method Considering FrequencyCharacteristics

The above mentioned embodiment is a method of multiplying thedetermined-estimated RRO waveform by an optimum gain K and adding theresult to RroTable. In other words, a uniform gain K is multiplied toall the frequency areas without considering the frequencycharacteristics of RRO and NRRO. However in an actual disk device, thefrequency characteristic is different between RRO and NRRO. In otherwords, the ratio of RRO and NRRO is different depending on thefrequency.

Therefore the σ of RRO and the σ of NRRO are determined for each degreeof RRO, and the optimum gain K can be determined from that ratioaccording to the above mentioned expression (21) or (24). FIG. 25 is aflow chart depicting the optimum gain calculation processing of thesecond embodiment of the present invention. In this description, it isassumed that the degree of the RRO is m, and m=1 to Ns/2 according tothe Nyquist theorem.

(S60) First just like step S10 in FIG. 10, the power spectrum of the RROis determined. The power spectrum of RRO targets a plurality of tracksin a zone. RRO is determined not for such a small number of tracks as“2” and “4”, but for several tens or several hundreds of tracks. The RROwaveform may be determined by multiplying RPE by the inversecharacteristic of the sensitivity function. Or a waveform which does notfollow-up RRO may be generated in each track taking sufficient time.After determining the RRO of each track in this way, all the RROwaveforms are lined up in a row and the power spectrum is determined.

(S62) Then the power spectrum of NRRO is determined. Just like FIG. 12,the position error ‘e’ is observed by an FFT analyzer, and the powerspectrum of RPE+NRPE is determined, then RPE is subtracted from theresult to determined NRPE. And the result is multiplied by the inversecharacteristic of the sensitivity function. Or the locus RroTable whereRRO is ignored may be generated taking sufficient time, and the powerspectrum of NRPE may be determined after suppressing RPE in the positionerror ‘e’ to almost zero.

(S64) Then the RRO degree m is initialized to “1”.

(S66) Then the power spectrums of RRO and NRRO are multiplied by thefrequency characteristic of DFT computation. In DFT computation, sin andcos are multiplied as shown in expression (26). The target degree m isdetermined, and a signal is supplied-at every predetermined frequencyinterval in the frequency area to be observed, that is 0 Hz to (samplingfrequency/2), and the power spectrum of RRO PowerRro (m) and the powerspectrum of NRRO PowerNrro (m), which are the output characteristics ofDFT, are determined. These become the frequency characteristics of thedetection characteristics of DFT computation.

FIG. 26 shows an example of the frequency characteristics of DFTcomputation. In FIG. 27, the power spectrum of NRRO that follows up thefrequency characteristics in FIG. 26 is shown by a solid line, and thepower spectrum of NRRO for each RRO degree is shown by circles. In FIG.28, the power spectrum of RRO is shown by a solid line, and the powerspectrum of RRO for each RRO degree is shown by circles. In FIG. 29, theRRO and NRRO power spectrums for each RRO degree in FIG. 27 and FIG. 28are overlaid in a same graph. In this example, the power spectrumfollows up the first–fourth degree RRO. In this way, the power spectrumof NRRO and the power spectrum of RRO are determined for each RROdegree.

(S68) Comparing these two spectrums, the ratio r (m) of the a of RRO andthe a of NRRO is determined for each RRO degree.

(S70) Applying this ratio r (m) to the above mentioned optimum conditionexpress (21) or (24), the optimum gain Krro (m) or Krro (M, m) of eachRRO degree is calculated. FIG. 30 is a graph depicting the optimum gaincharacteristic with respect to each RRO degree. In this example, thenumber of rotations for averaging N=1, and the number of repeats M=1. Asthe bottom graph in FIG. 30 shows, the RRO residual rate after RROcorrection for each RRO degree can also be determined. From thisresidual rate and original RRO power spectrum, the residual rates of RRObefore and after correction for all frequencies can be determined.

(S72) As mentioned above, the RRO degree m is incremented “1”, and it isjudged whether the RRO degree m is an observable Nyquist frequency(Ns/2) or more. If the RRO degree m is not more than (Ns/2), processingreturns to step S66, and the optimum gain Krro (m) or Krro (M, m) ofeach RRO degree, described in FIG. 27 to FIG. 30, is calculated. If theRRO degree m is an observable Nyquist frequency (Ns/2) or more,processing ends.

As described above, the gain for each RRO degree can be determined. Thisgain can be applied to the conventional method of calculating Rro orURro using DFT and inverse DFT. For example, the expression (28) in FIG.13 is transferred to the following expression (30) considering the RROdegree.

$\begin{matrix}{{{RRO}(q)} = {\sum\limits_{m = 1}^{{N_{S}/2} - 1}{\left\{ {{C\; 2(m){\cos\left( {2\pi\;{{mq}/N_{S}}} \right)}} + {S\; 2(m){\sin\left( {2\pi\;{{mq}/N_{S}}} \right)}}} \right\} \cdot {{Krro}(m)}}}} & (30)\end{matrix}$

In this case, RroTable (q) is calculated regarding gain K in step 30 as“1” in FIG. 13.

Now examples will be described. FIG. 31 is an RPE waveform diagrambefore and after RRO correction in the disk device in FIG. 1. For theRRO correction method, the addition gain Krro (m) is changed for each ofthe above mentioned frequencies. In FIG. 31, the index signal, the RPEwaveform before correction, and the RPE waveform after correction areshown sequentially from the top. Here the number of rotations foraveraging N=1 and the number of repeats M=1. In this example, a jump inRPE waveforms is observed at around the center. However this iseffectively removed after RRO correction.

FIG. 32 is a table showing a comparison of a method of setting a uniformaddition gain for all the frequencies and a method of changing theaddition gain for each RRO degree. The rate (residual rate) aftercorrection/before correction is determined for three values: RPE, RROand RPE+RRO. For the conditions, the number of repeats M=1, and sixtypes of rotations for averaging N: “1”, “2”, “3”, “4”, “6” and “8” areused.

In the case of the method of setting a uniform addition gain for all thefrequencies, the residual rate to be the minimum is determined whilechanging the addition gain K, as shown in FIG. 15 and FIG. 16. Forexample, in the case of N=1 and M=1 in FIG. 15, the residual rate of RPEis the minimum value=0.57 at K=0.70, the residual rate of RRO is theminimum value=0.734 at K=0.45, and the residual rage of RPE+RRO is theminimum value=0.488 at K=0.80.

In the same way, in the case of N=8 and M=1 in FIG. 16, the residualrate of RPE is the minimum value=0.247 at K=0.95, the residual rate ofRRO is the minimum value=0.392 at K=0.85, and the residual rate ofRPE+RRO is the minimum value=0.208 at K=1.00. In other words, theoptimum gain at which the residual rate becomes the minimum iscompletely different in RPE, RRO and RPE+RRO.

In the case of the method of changing the addition gain for each RROdegree, on the other hand, values are measured under the same conditionsfor all of RPE, RRO, and RPE+RRO. As the values of the residual rate inFIG. 32 show, the residual rate is smaller in the method of changing theaddition gain for each RRO degree than in the method of setting auniform addition gain for all the frequencies.

Then the effect of RRO correction on the entire surface of the disk isdetermined. FIG. 33 shows the result before RRO correction, and FIG. 34shows the result after RRO correction. In this example, RRO correctionconditions are that the addition gain is optimized for each RRO degree,the number of rotations for averaging N=3 and the number of repeats M=1.Also the addition gain is optimized at the outermost track on one sideof the disk, and the result is applied to the entire face of the disk.RPE of each track before correction and after correction is determinedin the number of track units, averaging 32 rotations. Using the maximumvalue of the absolute value thereof as the representative value of thetrack, this value is determined for all the tracks. The top graph inFIG. 33 and FIG. 34 are the number of points (number of tracks) of eachRPE indicated as histograms. The middle graph shows the probabilitydistribution to indicate the established value of each RPE, and thebottom graph shows the log10 (1−probability value of middle graph)=errorrate.

In the case when RRO correction in FIG. 34 is performed, it is shownthat the RPE value and the error rate dramatically increased in generalcompared with the status before RRO correction in FIG. 33. In this way,even with a very small number of measurement rotations, such as 3, RROcorrection can be effectively implemented.

Another RRO Correction Table Creation Method Considering CorrelationBetween Tracks

The above-mentioned method is based on the assumption that nocorrelation exists between the tracks of a disk. However the correlationof RRO between tracks may increase in some cases. For example, when adisk is mechanically distorted, some improvement is required in additionto a method of determining the Rro correction value at one point or ineach zone on the disk face. With the foregoing in view, an embodiment tosupport such a status will be described. In other words, a RroTablevalue is created in each track.

FIG. 35 is a flow chart depicting RRO correction table creationprocessing considering the correlation between tracks, and FIG. 36 andFIG. 37 describe the processing flow.

(S80) As FIG. 36 shows, the disk 4 with the same head is divided into aplurality of zones Z1, Z2 and Z3. First a common RRO correction value iscreated within the zone. In other words, the target head is moved to thetarget zone of the disk 4, and the RroTable value is initialized to “0”.An average RPE waveform of the sampling target track within the zone isdetermined, and the zone average RRO correction waveform RroZone iscalculated, setting an addition gain uniform for all frequencies as “1”.

(S82) Then the head is positioned to a measurement point (e.g. eachtrack) within the zone using this RroZone as an initial value, and theRroZone value is stored in the RroTable 29 as shown in FIG. 37.

(S84) The position error ‘e’ of the current track after moving ismeasured for a specified number of rotations N, and RPE is calculated,as mentioned above. And different addition gains are set for eachfrequency, as described in FIG. 25, and the RRO correction waveform Rro(q) is calculated by expression (30). And as FIG. 37 shows, the Rrocorrection value of the current track is stored in the RroTable 29. Inthe case of an example where the magnetic head 3 has an MR head as theread element, in addition to a write element, and a rotary actuator isused, the position of the write element and read element for the trackare different. Therefore in RroTable 29 in FIG. 37, the RRO value of theread element is measured and stored as RRO (R), independently from theRRO value of the write element, which is RRO (W).

(S86) Then it is judged whether all the measurement points within thezone have been measured. If all the measurement points within the zonehave not been measured, the head is moved to the next measurement point,and processing returns to step S84. If all the measurement points withinthe zone have been measured, creation of RroTable in the zone ends.

This is repeated for the number of divided zones shown in FIG. 36, andthe RroTable 29 in FIG. 37 is created. In this way, the disk 4 with asame head is divided into a plurality of zones, and a common RROcorrection value in the zone is calculated first, and the zone averageRRO correction waveform RroZone is calculated with setting an additiongain uniform for all the frequencies as “1”. Then using this RroZone asthe initial value, the head is moved to a measurement point in the zone(e.g. each track), and measurement is performed for a specified numberof rotations N, RPE is calculated, and a different addition gain is setdepending on the frequency, and the RRO correction waveform Rro (q) ismeasured by expression (30).

Therefore when the correlation of RRO between tracks is high, such asthe case when the disk is mechanically distorted, an Rro correctionvalue of the measurement point in each track can be measured, and anaccurate RRO correction is possible, even in such a status.

Servo Track Writing Method Using RRO Correction Table

Now an embodiment of using the correction table created as above will bedescribed. The first embodiment is for manufacturing the disk devicedescribed in FIG. 8. The disk where servo signals are externallyrecorded is installed in the disk device, and a correction table for allthe tracks is generated for each read and write position. Or a pluralityof tracks may constitute a zone and common components within the zonemay be corrected.

The second embodiment is used when servo signals are recorded in thedisk device. FIG. 38 is a diagram describing this. A servo signalrecording method is a self-servo writing method. As FIG. 38 shows,several tracks of servo signal SV1 are recorded with a predeterminedfeeding width at the edges (outer track in this case) of the disk 4.Then based on these servo signals SV1, the servo signals SV2 arerecorded in an area where the servo signals are not recorded on the disk4.

When the servo signals SV1 are recorded at the edge of the disk 4 (outertrack in this case), the RRO correction value is measured, and usingthis RRO correction value, the servo signals SV2 are recorded in an areawhere the servo signals are not recorded on the disk 4, based on theservo signals SV1. And the RRO correction value is measured for all thetracks, and the RroTable 29 is created.

The third embodiment is used for a servo signal recording method calledcopy STW or rewrite STW. FIG. 39 is a diagram depicting the servo trackwriting method. AS FIG. 39 shows, servo signals are recorded on theentire face of at least one side of the disk 4-1 in advance, and thedisk 4-1 where servo signals are recorded and a disk 4-2 where servosignals are not recorded are installed on the disk device.

And while positioning control is performed using the servo signals onone side of the disk 4-1, the RRO correction value is measured, andusing this RRO correction value, servo signals are recorded on the facewhere servo signals have not yet been recorded (rear side of the disk4-1 and the disk 4-2). And RroTable 29 is created by measuring the RROcorrection values of all the tracks. In this case, servo signals mayalso be rewritten on the side of the disk 4-1 where the servo signalshave been recorded from the beginning, using the RRO correction value,and the original servo signals may be deleted later.

The fourth embodiment is to be used after shipping the disk device. Whenthe servo signals reach a status which is different from that duringmanufacturing, such as the case of an eccentricity due to mechanicaldeformation or loss of servo signals due to a media scratch, the fourthembodiment is used to generate signals that follow-up or do notfollow-up RRO. This makes a highly accurate correction possible with asmall number of times of rotation. FIG. 40 is a flow chart depictingthis correction table rewriting method.

(S90) The MCU 14 of the disk device judges whether a positioningaccuracy abnormality occurred. For example, when the head cannot bepositioned at the target track center (position error is more than offtrack standard value) even after positioning control using theabove-mentioned RRO correction table 29, a retry is performed. If thehead cannot be positioned at the target track center even after severaltimes of retry, it is judged that the positioning accuracy is abnormal.

(S92) If it is judged as a positioning accuracy abnormality, it is thenjudged whether recovery is possible by RRO correction. For example, ifthe head detection capability is dropped, recovery is not possible evenif RRO correction is performed. If it is judged that recovery ispossible by RRO correction, the MCU 14 measures the RRO correctionvalues, as mentioned above.

(S94) Then it is judged whether rewriting of the RRO correction table 29is effective by comparing the RRO correction value measurement resultand the correction values of the current RRO correction table 29. Forexample, if the RRO correction value measurement result and thecorrection values of the current RRO correction table 29 are not verydifferent, positioning accuracy does not improve even if the correctiontable 29 is rewritten, so processing ends. If the RRO correction valuemeasurement result and the correction values of the current RROcorrection table 29 are different, positioning accuracy improves byrewriting the correction table 29. So the correction table 29 isrewritten, and processing ends.

In this way, when the servo signals reach a status which is differentfrom that during manufacturing, such as the case when an eccentricity isgenerated due to mechanical deformation or the servo signals are lostdue to a media scratch, the servo signals can be rewritten to be signalsthat follow-up or that do not follow-up RRO, which can contribute toimproving the positioning accuracy.

Other Embodiments

There are some possible locations where the above correction data(table) can be recorded. As FIG. 41 shows, the correction data RroTable(q) may be added at the end of the servo signals in each sector. Orcorrection data may be recorded in a dedicated area on the disk 4 mediumthat is not used for recording/regenerating data. Also the correctiondata may be recorded in a non-volatile memory on an electronic circuitof the disk device in advance.

Of these three recording locations, the first or the second method iseffective when all the individual tracks are corrected. If only thetrack of which the positional fluctuation is large is corrected, that isthe correction data volume is small, then the third method (non-volatilememory) may be used.

The above method is effective when the disk of the disk device is fixed.That is, the case when the media is not replaceable. Even in the casewhen the disk is fixed in a magnetic disk device, such as a magnetictransfer and patterned media, if servo signals on the media are formedusing a common die, a common RRO, which is determined depending on thedie creation accuracy, can be measured and the disk can be used asmedia.

The disk device was described as a magnetic disk device, but the presentinvention can be applied to other disk media, such as an optical diskdevice and magneto-optical disk device. In the same way, RRO was usedfor description of the embodiments in FIG. 25 to FIG. 41, and thepresent invention can also be applied to the URRO described in FIG. 21to FIG. 24. The present invention was described using the embodiments,but various modifications are possible for the present invention withinthe scope of the essential character of the present invention, whichshall not be excluded from the scope of the present invention.

Since an adjusted gain, based on the ratio of the magnitude between thecomponents synchronizing rotation of the disk and the components notsynchronizing rotation of the disk in the position signals, is used, again to minimize RRO after correction can be theoretically determinedusing an expression for determining RRO after correction. Therefore gaincan be determined without depending on experiment, and the value of RROafter correction can be guaranteed, and the manufacturing time anddevice specifications can be determined. Therefore a disk device whichrequires rotation synchronization correction can be manufactured in ashorter time, and disk devices suitable for mass production can beimplemented at low cost.

1. A correction table creation method for head position control forcreating correction values for correcting components synchronizingrotation of a disk of a disk device that controls a position of a headfor at least reading information of the disk using position signals ofsaid disk, comprising steps of: measuring position error componentssynchronizing the rotation of said disk from an average waveform of saidposition signals for a plural number of rotations of said disk;correcting said measured position error components using an adjustedgain based on a ratio of the magnitude between components synchronizingrotation of said disk and components not synchronizing rotation of saiddisk in said position signals and said number of rotations; and storingsaid corrected position error components in the correction table.
 2. Thecorrection table creation method for head position control according toclaim 1, wherein said correction step further comprises a step ofcorrecting said measured position error components using an adjustedgain based on the number of measurement rotations for averaging saidposition signals, the number of repeats of said correction, and theratio of the magnitude between components synchronizing rotation of saiddisk and components not synchronizing rotation of said disk in saidposition signals.
 3. The correction table creation method for headposition control according to claim 1, further comprising: a step ofmeasuring the normal distribution of components synchronizing rotationof said disk and the normal distribution of components not synchronizingrotation of said disk in said position signals; and a step ofcalculating said adjusted gain based on the ratio between the normaldistribution of said synchronizing components and the normaldistribution of said not synchronizing components.
 4. The correctiontable creation method for head position control according to claim 1,wherein said correction step further comprises a step of correcting saidmeasured position error components for each repeat using a gain for eachrepeat, that is an adjusted gain based on the number of measurementrotations for averaging said position signals, the number of repeats ofsaid correction, and the ratio of the magnitude between the componentssynchronizing rotation of said disk and the components not synchronizingrotation of said disk in said position signals.
 5. The correction tablecreation method for head position control according to claim 1, whereinsaid correction step further comprises a step of correcting saidmeasured position error components using adjusted gains for eachfrequency that is multiple of the rotation frequency of said disk, saidgains are acquired by determining the ratios of the magnitude betweenthe components synchronizing rotation of said disk and the componentsnot synchronizing rotation of said disk in said position signals foreach said frequency.
 6. The correction table creation method accordingto claim 1, wherein said correction step comprises: a step of executinga DFT (Digital Fourier Transformation) of said measured position errorcomponents; a step of multiplying said DFT results by a transferfunction of a position control system; a step of executing an inverseDFT of said multiplied results; and a step of multiplying said inverseDFT results by said adjusted gain.
 7. A correction table creation methodfor head position control for creating correction values for correctingcomponents synchronizing rotation of a disk of a disk device thatcontrols a position of a head for at least reading information of thedisk using position signals of said disk, comprising steps of: measuringposition error components synchronizing the rotation of said disk froman average waveform of said position signals; correcting said measuredposition error components using an adjusted gain based on the number ofmeasurement rotations for averaging said position signals, the number ofrepeats of said correction, and a ratio of the magnitude between thecomponents synchronizing rotation of said disk and components notsynchronizing rotation of said disk in said position signals; andstoring said corrected position error components in the correctiontable, wherein in said storage step, the residual RRO σ, that is anormal distribution of components synchronizing rotation of a diskcorrected by the correction value stored in said correction table,follows the following expression (18), where the normal distribution ofcomponents synchronizing rotation of said disk is σ RRO, the normaldistribution of components not synchronizing rotation of said disk is σNRRO, said number of measurement rotations is N, said number of repeatsis M, and said gain is K, $\begin{matrix}{\left( {{residualRRO}\mspace{14mu}\sigma} \right)^{2} = {{\left( {1 - K} \right)^{2M}\sigma_{RRO}^{2}} + {{K^{2}/N}{\sum\limits_{i = 1}^{M}{\left( {1 - K} \right)^{2{({i - 1})}}\sigma_{NRRO}^{2}}}}}} & (18)\end{matrix}$
 8. A disk device, comprising: a head for at least readinginformation of a disk; an actuator for moving said head to a desiredposition on said disk; a correction table for storing correction signalsacquired by measuring position error components synchronizing rotationof said disk from an average waveform of position signals from said headfor a plural number of rotations of said disk and correcting saidmeasured position error components using an adjusted gain based on aratio of the magnitude between the components synchronizing rotation ofsaid disk and the components not synchronizing rotation of said disk insaid position signals and said number of rotations; and a control unitfor calculating an error between a target position and a currentposition based on the position signals from said head and controllingsaid head position based on said position error and said correctionsignals.
 9. The disk device according to claim 8, wherein saidcorrection table stores said correction signals by correcting saidmeasured position error components using an adjusted gain based on thenumber of measurement rotations for averaging said position signals, thenumber of repeats of said correction, and the ratio of the magnitudebetween the components synchronizing rotation of said disk and thecomponents not synchronizing rotation of said disk in said positionsignals.
 10. The disk device according to claim 8, wherein said controlunit measures the normal distribution of components synchronizingrotation of said disk and the normal distribution of components notsynchronizing rotation of said disk in said position signals, andcalculates said adjusted gain based on the ratio between the normaldistribution of said synchronizing components and the normaldistribution of said not synchronizing components.
 11. The disk deviceaccording to claim 8, wherein said correction table stores saidcorrection signals acquired by correcting said measured position errorcomponents for each repeat using a gain for each repeat, that isadjusted based on the number of measurement rotations for averaging saidposition signals, the number of repeats of said correction, and theratio of the magnitude between the components synchronizing rotation ofsaid disk and the components not synchronizing rotation of said disk insaid position signals.
 12. The disk device according to claim 8, whereinsaid correction table stores said correction signals acquired bycorrecting said measured position error components using adjusted gainsfor each freciuency that is a multiple of the rotation frequency of saiddisk, said gains are acquired by determining the ratio of the magnitudebetween the components synchronizing rotation of said disk and thecomponents not synchronizing rotation of said disk in said positionsignals for each said frequency.
 13. The disk device according to claim8, wherein said control unit subtracts said correction signal from saidposition error and generates said head position control signal from saidsubtracted position error.
 14. The disk device according to claim 8,wherein said control unit subtracts said correction signal from saidhead position control signal acquired from said position error so as tocontrol said head position.
 15. A disk device comprising: a head for atleast reading information of a disk; an actuator for moving said head toa desired position on said disk; a correction table for storingcorrection signals acquired by measuring a position error componentssynchronizing rotation of said disk from an average waveform of positionsignals from said head for a plural number of rotations of said disk andcorrecting said measured position error components using an adjustedgain based on a ratio of the magnitude between the componentssynchronizing rotation of said disk and the components not synchronizingrotation of said disk in said position signals and said number ofrotation; and a control unit for calculating an error between a targetposition and a current position based on the position signals from saidhead and controlling said head position based on said position error andsaid correction signals; wherein the residual RRO σ, that is a normaldistribution of components synchronizing rotation of a disk corrected bythe correction value stored in said correction table, follows thefollowing expression (18), where the normal distribution of componentssynchronizing rotation of said disk is σ RRO, the normal distribution ofcomponents not synchronizing rotation of said disk is a σ NRRO, saidnumber of measurement rotations is N, said number of repeats is M, andsaid gain is K, $\begin{matrix}{\left( {{residualRRO}\mspace{14mu}\sigma} \right)^{2} = {{\left( {1 - K} \right)^{2M}\sigma_{RRO}^{2}} + {{K^{2}/N}{\sum\limits_{i = 1}^{M}{\left( {1 - K} \right)^{2{({i - 1})}}\sigma_{NRRO}^{2}}}}}} & (18)\end{matrix}$
 16. A head position control device for controlling aposition of a head for at least reading information of a disk usingsignals acquired by correcting the position signals of said disk bycomponents synchronizing rotation of said disk, comprising: a correctiontable for storing correction signals acquired by measuring positionerror components synchronizing rotation of said disk from an averagewaveform of said position signals for a plural number of rotations ofsaid disk and correcting said measured position error components usingan adjusted gain based on the ratio of the magnitude between componentssynchronizing rotation of said disk and components not synchronizingrotation of said disk in said position signals and said number ofrotations; and a controller for calculating an error between a targetposition and a current position based on the position signal from saidhead; reading correction signals from said correction table andcontrolling said head position based on said position error and saidcorrection signals.
 17. The head position control device according toclaim 16, wherein said correction table stores said correction signalsacquired by correcting said measured position error components using again, that is adjusted based on the number of measurement rotations foraveraging said position signals, the number of repeats of saidcorrection, and the ratio of the magnitude between componentssynchronizing rotation of said disk and the components not synchronizingrotation of said disk in said position signals.
 18. The head positioncontrol device according to claim 16, said controller measures thenormal distribution of components synchronizing rotation of said diskand the normal distribution of components not synchronizing rotation ofsaid disk in said position signals, and calculates said adjustment gainbased on the ratio between the normal distribution of said synchronizingcomponents and the normal distribution of said not synchronizingcomponents.
 19. The head position control device according to claim 18,wherein said controller executes a DFT (Digital Fourier Transformation)of said measured position error components, multiplies said DFT resultsby a transfer function of a position control system, executes an inverseDFT of said multiplied result and multiplies said inverse DFT results bysaid adjusted gain.
 20. The head position control device according toclaim 16, wherein said controller reads said correction signal from thecorrection table acquired by correcting said measured position errorcomponents for each of said repeats using a gain for each repeat, thatis adjusted based on the number of measurement rotations for averagingsaid position signals, the number of repeats of said correction, and theratio of the magnitude between the components synchronizing rotation ofsaid disk and the components not synchronizing rotation of said disk insaid position signals.
 21. The head position control device according toclaim 16, wherein said controller reads said correction signals from thecorrection table acquired by correcting said measured position errorcomponents, using adjusted gains for each frequency that is a multipleof the rotation frequency of the disk, wherein said gains are acquiredby determining the ratios of the magnitude between the componentssynchronizing rotation of said disk and the components not synchronizingrotation of said disk in said position signals for each frequency. 22.The head position control device according to claim 16, wherein saidcontroller subtracts said correction signal from said position error andgenerates said head position control signal from said subtractedposition error.
 23. The head position control device according to claim16, wherein said controller subtracts said correction signal from saidhead position control signal acquired from said position error so as tocontrol said head position.
 24. A head position control device forcontrolling a position of a head for at least reading information of adisk using signals acquired by correcting the position signals of saiddisk by components synchronizing rotation of said disk, comprising: acorrection table for sorting correction signals acquired by measuringposition error components synchronizing rotation of said disk from anaverage waveform of said position signals for a plural number ofrotations of said disk and correcting said measured position errorcomponents using an adjusted gain based on the ratio of the magnitudebetween components synchronizing rotation of said disk and componentsnot synchronizing rotation of said disk in said position signals andsaid number of rotations; and a controller for calculating an errorbetween a target position and a current position based on the positionsignal from said head, reading correction signals from said correctiontable and controlling said head position based on said position errorand said correction signals, wherein the residual RRO σ, that is anormal distribution of components synchronizing rotation of a diskcorrected by the correction value stored in said correction table,follows the following expression (18), where the normal distribution ofcomponents synchronizing rotation of said disk is σ RRO, the normaldistribution of components not synchronizing rotation of said disk is σNRRO, said number of measurement rotations is N, said number of repeatsis M, and said gain is K, $\begin{matrix}{\left( {{residualRRO}\mspace{14mu}\sigma} \right)^{2} = {{\left( {1 - K} \right)^{2M}\sigma_{RRO}^{2}} + {{K^{2}/N}{\sum\limits_{i = 1}^{M}{\left( {1 - K} \right)^{2{({i - 1})}}\sigma_{NRRO}^{2}}}}}} & (18)\end{matrix}$
 25. A correction table creation method for head positioncontrol for creating values for correcting components synchronizingrotation of a disk of a disk device that controls a position of a headfor at least reading information of the disk using position signals ofsaid disk, comprising steps of: measuring position error componentssynchronizing the rotation of said disk from an average waveform of saidposition signals in plural divided zones of a single disk surface;correcting said measured position error components using a singleadjusted gain; storing said corrected position error components of eachof said zones in the correction table; measuring position errorcomponents synchronizing the rotation of said disk from an averagewaveform of said position signals in each track in said divided zone;correcting said measured position error components of said each trackusing adjusted gains for each frequency that is a multiple of therotation frequency of said disk, and said adjusted gains are based onratios of the magnitude between components synchronizing rotation ofsaid disk and components not synchronizing rotation of said disk in saidposition signals for each said frequency; and storing said correctedposition error components of each said track in the correction table.26. A head position control device for controlling a position of a headfor at least reading information of a disk using signals acquired bycorrecting the position signals of said disk by components synchronizingrotation of said disk, comprising: a correction table for storing afirst correction signal of each zone acquired by measuring positionerror components synchronizing the rotation of said disk from an averagewaveform of said position signals in plural divided zones of a singledisk surface and correcting said measured position error componentsusing a single adjusted gain, and a second correction signal of eachtrack by measuring position error components synchronizing the rotationof said disk from an average waveform of said position signals in eachtrack in said divided zone and correcting said measured position errorcomponents of said each track using adjusted gains for each frequencythat is a multiple of the rotation frequency of said disk, and saidadjusted gains are based on ratios of the magnitude between componentssynchronizing rotation of said disk and components not synchronizingrotation of said disk in said position signals for each said frequency;and a controller for calculating an error between a target position anda current position based on the position signal from said head, readingsaid first and second correction signals from said correction table andcontrolling said head position based on said position error and saidfirst and second correction signals.
 27. A head position control devicefor moving a head for at least reading information of a disk to adesired position on said disk by using an actuator, comprising: acorrection table for storing correction signals acquired by measuring aposition error components synchronizing rotation of said disk from anaverage waveform of position signals from said head and correcting saidmeasured position error components using an adjusted gain based on aratio of the magnitude between the components synchronizing rotation ofsaid disk and the components not synchronizing rotation of said disk insaid position signals; and a control unit for calculating an errorbetween a target position and a current position based on the positionsignals from said head and controlling said head position based on saidposition error and said correction signals, wherein said control unitmeasures said position error components synchronizing rotation of saiddisk from said average waveform of position signals from said head andcorrects said measured position error components using said adjustedgain, judges whether or not to rewrite said correction table accordingto said corrected position errors and said correction signals in saidcorrection table, and rewrites said correction table to said correctedposition errors when judging to perform said rewrite.
 28. A headposition control method for moving a head for at least readinginformation of a disk to a desired position on said disk by using anactuator, comprising: a step of measuring position error componentssynchronizing rotation of said disk from an average waveform of positionsignals from said head; a step of correcting said measured positionerror components using an adjusted gain based on a ratio of themagnitude between the components synchronizing rotation of said disk andthe components not synchronizing rotation of said disk in said positionsignals; a step of calculating an error between a target position and acurrent position based on the position signals from said head; a step ofcontrolling said head position based on said position error and saidcorrection signals; a step of re-measuring said position errorcomponents synchronizing rotation of said disk from said averagewaveform of position signals from said head; a step of correcting saidmeasured position error components using said adjusted gain; a step ofjudging whether or not to rewrite said correction table according tosaid corrected position errors and said correction signals in saidcorrection table; and rewriting said correction table to said correctedposition errors when judging to perform said rewrite.